JP5372682B2 - Surface effect 3D photonic crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a three-dimensional photonic crystal which is easily accessed from the outside, is not influenced by an optical loss due to absorption or the like, and controls light propagation, light localization or the like. <P>SOLUTION: The surface effect three-dimensional photonic crystal 30 is configured by forming a surface structure layer 31, which is different in structure from an original crystal surface, on the surface of a wood-pile three dimensional photonic crystal. The surface structure layer 31 has an orthogonal grid structure that is formed by adding a connection member 32 formed of the same material as a rod 11 to a stripe layer 12 which is originally formed on the crystal surface, into the same layer, in the direction orthogonal to the rod 11 composing the stripe layer. The connection member 32 is formed at a position at which the surface structure layer 31 shifts by 1/2 cycle from the rod of the most adjacent stripe layer 125. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a three-dimensional photonic crystal that can be easily accessed from the outside and can control light propagation and light confinement without being affected by light loss due to absorption or the like.

  In recent years, photonic crystals have attracted attention as new optical devices. A photonic crystal is an optical functional material having a periodic refractive index distribution and forms a band structure with respect to energy of light or electromagnetic waves. In particular, an energy region (photonic band gap, abbreviated as PBG) where light or electromagnetic waves cannot be propagated is formed.

  By introducing a disorder (defect) of the refractive index distribution into the refractive index distribution of the photonic crystal, an energy level (defect level) due to this defect is formed in the PBG. As a result, only light having a wavelength corresponding to the energy of the defect level in the PBG can exist at this defect position. As a result, an optical circuit element such as an optical resonator composed of point-like defects or an optical waveguide composed of linear defects can be provided in the photonic crystal. By providing a large number of these optical circuit elements in one photonic crystal to constitute an optical integrated circuit, this photonic crystal becomes an optical IC element. Until now, discrete optical circuit elements have been individually connected and used in the field of optical communication and the like, but the circuit can be miniaturized by using an optical IC element.

  Photonic crystals include two-dimensional photonic crystals and three-dimensional photonic crystals. Among these, the three-dimensional photonic crystal is structurally robust compared to the two-dimensional photonic crystal, and has a feature that it can cope with the polarization state of all light. In Patent Document 1, a plurality of stripe layers formed by periodically arranging rods made of a material having a refractive index higher than that of air are periodically stacked, and rods of the adjacent stripe layers are orthogonal to each other. In addition, a woodpile type three-dimensional photonic crystal having a structure in which rods of the next adjacent stripe layers are parallel and shifted by a half period is described. This document also describes that an optical waveguide is formed by providing a linear defect in a part of the rod inside the three-dimensional photonic crystal.

  Patent Document 2 describes a three-dimensional photonic crystal in which point defects are provided in a rod inside a structure. In this point defect, a part of the rod is missing and an object with a different shape or refractive index is placed there, a member attached to the rod without losing the rod, or the shape of the rod itself is changed. (Thickened / thinned), etc. This point defect becomes an optical resonator that resonates with light of a predetermined frequency determined by its shape and size, and position (displacement) with respect to the rod. This optical resonator becomes a component of the optical IC element as described above. Further, by introducing a light emitter into the defect portion, it can also be used as a laser light source in which light resonates and emits light at a point defect.

JP 2001-074955 A JP 2004006567 A

  As described above, in the conventional three-dimensional photonic crystal, defects used for an optical resonator, an optical waveguide, and the like are formed (embedded) inside the structure. Accordingly, there are two types of access to light between inside and outside, such as taking light outside the structure into the structure, and taking out light inside the structure outside the structure, and control and operation of light inside the structure. There was a problem that it was difficult compared to a two-dimensional photonic crystal.

  The problem to be solved by the present invention is to provide a three-dimensional photonic crystal that is easy to access from the outside and is free from the effects of light loss due to absorption, etc., and that can control light propagation and light confinement. is there.

  The inventor of the present application has paid attention to the “surface” of the three-dimensional photonic crystal as a result of repeated research to solve the above-described problems. Since the surface of the three-dimensional photonic crystal has a free space such as air on one side, it is extremely easy to cause various substances to interact with light. However, in the field of three-dimensional photonic crystals, optical manipulation on the surface has not been studied at all.

  The inventor of the present application first examined whether a localized state of light is formed on the surface of the three-dimensional photonic crystal from both theory and experiment. As a result, it was confirmed that a light state (mode) was formed on the surface of the three-dimensional photonic crystal. As a result of various experiments based on this, it is impossible to propagate light on the surface of the three-dimensional photonic crystal by changing the surface structure of the three-dimensional photonic crystal while maintaining a predetermined relationship with the internal structure. It was found that PBG (hereinafter referred to as “surface mode gap”) is formed. Furthermore, it has been found that an optical resonator or an optical waveguide is formed by introducing point-like or linear defects into a layer whose surface structure has been changed (hereinafter referred to as “surface structure layer”).

That is, the three-dimensional photonic crystal according to the present invention is
One or a plurality of layers on the surface of a three-dimensional photonic crystal having a periodic structure in which stripe layers in which rods are arranged in parallel with each other at a predetermined period length are stacked so that rods of the adjacent stripe layers are orthogonal to each other The surface structure layer made of a stripe layer has a connecting member for connecting adjacent rods in the stripe layer, and the connecting member is arranged in the longitudinal direction of the rod at the periodic length, whereby the surface structure wherein the photonic band gap layers are formed.
In order to clarify the difference between the three-dimensional photonic crystal according to the present invention and the conventional three-dimensional photonic crystal, the three-dimensional photonic crystal according to the present invention in which the surface structure layer is formed will be described below. Is referred to as a “surface effect three-dimensional photonic crystal”.

The surface effect three-dimensional photonic crystal can further form an optical resonator or an optical waveguide by introducing a point defect or a line defect into the surface structure layer.

  The surface structure layer may be only one layer on the outermost surface of the three-dimensional photonic crystal, or may be composed of a plurality of layers near the surface including the outermost surface.

The surface effect three-dimensional photonic crystal according to the present invention is such that a PBG is formed in the surface structure layer by providing a surface structure layer having a predetermined relationship with the periodicity of the internal structure of the three-dimensional photonic crystal. . The surface structure layer, as in the conventional two-dimensional and three-dimensional photonic crystal, it is possible to form a like optical resonator and an optical waveguide by introducing defects such as point-like or linear, surface effects Light control and light manipulation on the surface of the three-dimensional photonic crystal are possible. In addition, since the optical resonator and the optical waveguide are formed on the structure surface, access to the outside light can be realized with higher efficiency than the conventional three-dimensional photonic crystal. Furthermore, since light confinement that is not affected by absorption or the like is possible on the surface of the surface-effect three-dimensional photonic crystal, high-sensitivity and high-level light-matter interaction without light loss can be obtained.

The perspective view which showed an example of the structure of a three-dimensional photonic crystal. The figure which showed the calculation result of the photonic band of the three-dimensional photonic crystal which has an infinite size without the surface, and the figure which showed the calculation result of the photonic band of the three-dimensional photonic crystal which has the surface (b). The figure which showed the calculation result of the state of the light in (GAMMA) -M direction of the three-dimensional photonic crystal surface. The schematic block diagram which shows the experimental system for investigating the localized state of the light in the three-dimensional photonic crystal surface. The figure which showed an example of the measurement result of the reflectance for each wavelength (frequency) when the incident angle is θ = 52.3 °, and the figure which shows the measurement result of the photonic band on the surface of the three-dimensional photonic crystal (b). The figure which showed propagation of light in the three-dimensional photonic crystal surface. The perspective view (a) which shows one Example of the surface effect three-dimensional photonic crystal which concerns on this invention, and the electron micrograph (b) of a surface structure layer. Band diagram (a) for the conventional surface structure, band diagram (b) when the width of the dielectric of the surface structure layer is 0.16a (= 0.08 μm) with respect to the rod interval a (= 0.5 μm), and the surface Band diagram (c) when the width of the dielectric of the structural layer is 0.4a (= 0.2 μm). The electron micrograph of the surface structure layer which formed the point-shaped surface defect. Figure (a) showing the calculation result of optical localization in surface defects, and the case where the width of the dielectric in the surface structure layer is 0.4a (= 0.2μm) and the width of the surface defects is 0.55a (= 0.275μm) The figure which showed the measurement result. The figure which showed the measurement result of the resonance spectrum at the time of changing the length of a surface defect. The figure which showed the length of the surface defect, and the change of Q value. The top view which showed the surface structure layer in which the waveguide was formed by providing a linear surface defect. The band figure which showed the waveguide mode of the waveguide formed in the surface structure layer. The band figure which showed the waveguide mode when the width | variety of a waveguide is 0.52a. The figure which showed the electric field distribution in the circumference | surroundings of a waveguide when the width | variety of a waveguide is 0.52a.

  The inventor of the present application first verified the state of light on the crystal surface from both theory and experiment as to whether or not optical manipulation on the surface of the three-dimensional photonic crystal is possible. This will be described with reference to FIGS.

  FIG. 1 is a perspective view of an example of the structure of a three-dimensional photonic crystal. The three-dimensional photonic crystal 10 in this perspective view is called a woodpile type, and has a stripe layer 12 in which rods 11 made of a dielectric such as Si or GaAs are arranged substantially in parallel with a period a. Has a laminated structure. The stripe layers 12 are laminated so as to have the same structure in a four-layer cycle, and the rod 11 of the 4n-th stripe layer 121 (n is an integer, the same applies hereinafter) and the rod 11 of the (4n + 2) -th stripe layer 123. Are arranged so as to be substantially parallel and shifted by 1/2 period. The relationship between the rod 11 of the (4n + 1) th stripe layer 122 and the rod 11 of the (4n + 3) th stripe layer 124 is the same. The rods 11 are arranged so as to be substantially orthogonal to each other between the adjacent stripe layers 12.

  FIG. 2 shows a result of calculating a photonic band by the three-dimensional time domain difference method for the woodpile type three-dimensional photonic crystal 10 described above. 2A is a band diagram when it is assumed that the surface does not exist in the three-dimensional photonic crystal 10 (the size is infinite), and FIG. 2B has a surface ( It is a band diagram in the case where the number of stacked stripe layers 12 is finite).

  As shown in FIG. 2 (a), when the size of the three-dimensional photonic crystal 10 is infinite, PBG having no light state is formed near the frequency of 0.29 to 0.34 (c / a). Light with a wavelength in the energy region cannot be present in the crystal. On the other hand, in the three-dimensional photonic crystal having the surface, it can be seen that the light mode 13 indicated by the broken line is formed in the frequency region where the PBG was formed in FIG. 2A (FIG. 2B). ). FIG. 3 shows the calculation result in the Γ-M direction of the surface of the three-dimensional photonic crystal used in FIG. From this figure, it can be seen that the electric field is strongly localized on the surface of the three-dimensional photonic crystal in the Γ-M direction. This indicates that light is present on the surface of the three-dimensional photonic crystal in the Γ-M direction.

  In order to verify the above results, whether or not a localized state of light is formed on the surface of the three-dimensional photonic crystal was verified by experiments. A schematic configuration of the experimental system used in this experiment is shown in FIG. The experimental system of FIG. 4 is a system in which a prism 20 is arranged in the very vicinity (˜0.5 μm) of the surface of the three-dimensional photonic crystal 10.

  When light enters the prism 20 of FIG. 4, the incident light enters the bottom surface 21 of the prism 20 at an angle θ. The light incident on the bottom surface is reflected at the same angle θ as the incident angle and is emitted as it is to the outside of the prism 20, but on the other hand, the bottom surface 21 is in a state where light is slightly exuded (attenuated wave). In the case where a light state exists on the surface of the photonic crystal 10, the exuded light is coupled to the surface of the photonic crystal, so that the reflected light intensity from the prism decreases.

  The results of this experiment are shown in FIG. FIG. 5A shows an example of the measurement result when the incident angle at the bottom surface 21 of the prism 20 is θ = 52.3 °, and shows the relationship between the wavelength and the reflectance (ratio of incident light intensity and reflected light intensity). FIG. In the result of this figure, a phenomenon was observed in which the reflectance decreased with respect to incident light having a frequency in the vicinity of 0.36 c / a. From this result, it can be seen that light is coupled to the surface of the three-dimensional photonic crystal 10. On the other hand, the measurement result of the photonic band obtained by changing the frequency of incident light and the incident angle θ with respect to the above experimental system is shown in FIG. The result of this figure agrees well with that of FIG. Therefore, it was found from both theory and experiment that a light state (mode) is formed on the surface of the photonic crystal (light is localized).

  FIG. 6 shows the results of an experiment in which the surface of the three-dimensional photonic crystal 10 is irradiated with laser light. Here, FIG. 6A shows a laser beam before irradiation with a laser beam, and FIG. 6B shows a region surrounded by a dotted line in FIG. 6A with an incident angle θ = 45.7 ° and a laser beam with a wavelength of 1430 nm. It is the figure which showed the measurement result of the state of the light in the three-dimensional photonic crystal surface after having performed. From this figure, when laser light having a wavelength corresponding to the photonic band on the surface is irradiated, it can be clearly seen that the light propagates to the surface of the three-dimensional photonic crystal 10 in addition to the irradiated region. Can do.

  From the above theoretical and experimental results, it has been found that there is a mode of light on the surface of the three-dimensional photonic crystal and that light propagates on the surface. However, since this light diffuses on the crystal surface, the light cannot be freely controlled on the three-dimensional photonic crystal surface as it is. In contrast, the inventor of the present application first considered the formation of a “surface mode gap” in which no light mode exists on the surface of the three-dimensional photonic crystal 10. As a result of various experiments, by forming a surface structure layer having a periodicity having a predetermined relationship with the periodicity of the internal structure on the surface of the three-dimensional photonic crystal, a surface mode gap is formed on the surface. I found out that Examples of the present invention are shown below.

An embodiment of the surface effect three-dimensional photonic crystal according to the present invention will be described with reference to FIGS.
FIG. 7A shows a perspective view of the surface effect three-dimensional photonic crystal 30 of the present embodiment. FIG. 7B is an electron micrograph of the surface structure layer 31 of the three-dimensional photonic crystal 30. The surface effect three-dimensional photonic crystal 30 is obtained by forming a surface structure layer 31 having a structure different from the original crystal surface on the surface of a woodpile type three-dimensional photonic crystal. The surface structure layer 31 is originally connected to the stripe layer 12 formed on the crystal surface in the same layer and made of the same material as the rod 11 in a direction perpendicular to the rod 11 constituting the stripe layer. This is a layer having an orthogonal lattice structure to which a member 32 is added. The connecting member 32 is formed at a position shifted from the rod 11 of the stripe layer 125 nearest to the surface structure layer 31 by a half period. The number of stacks in the surface effect three-dimensional photonic crystal of this example is 8, including the surface structure layer.

FIG. 8 shows the measurement result of the photonic band on the surface of the three-dimensional photonic crystal 30 when the width W of the connecting member 32 is changed. FIG. 8 (a) is a band diagram for a conventional surface structure in which the connecting member 32 is not added (W = 0), and FIGS. 8 (b) and 8 (c) are respectively W = 0.16a (= 0.08 μm). ) And 0.4a (= 0.2 μm). The period of the rod 11 and the connecting member 32 was a = 0.5 μm, and the rod width was 0.4a (= 0.2 μm).
In the band diagram of FIG. 8A, as in FIG. 5B, surface modes exist for all frequency bands (wavelength bands). On the other hand, it was found that when a connecting member 32 with W = 0.16a was added as shown in FIG. 8B, a surface mode gap was formed in the wavelength range of 1.3 to 1.4 μm. Further, when a connecting member 32 of W = 0.4a was added as shown in FIG. 8C, a surface mode gap was formed in the wavelength region of 1.4 to 1.5 μm.

Next, a result in the case where a dot-like “surface defect” is formed by disturbing a part of the structure of the surface structure layer 31 is shown. Figure 9 is an electron micrograph of the region of the length L _d to form surface defects 321 and W _d the width of the connecting member 32 from the W surface structure layer 31A. When a numerical calculation is performed on the three-dimensional photonic crystal 30 using the surface structure layer 31A, as shown in FIG. 10 (a), the light is localized in a dot-like manner only in the portion where the width _Wd is increased. I found out that it exists. Based on this result, an experiment was actually performed by setting the width of the connecting member 32 to W = 0.4a and the width of the surface defect 321 to W _d = 0.55a (= 0.275 μm). FIG. 10B shows the result of measuring the localized state of light in the region centered on the surface defect 321. As shown in this figure, it can be seen that light is localized only in a very narrow defect region of only a few μm or less.

Further, FIG. 11 shows the measurement result of the resonance spectrum when the length L _d of the surface defect 321 is changed. From FIG. 11, it was found that light having different wavelengths is stored in the surface defect depending on the length L _d of the surface defect 321. FIG. 12 shows the measurement results of the Q values of various surface localized modes. As can be seen from this figure, the maximum Q value reached 9000 or more at L _d = 6a. This value is the world's largest among three-dimensional photonic crystals. This Q value is expected to increase exponentially by increasing the number of stacked layers.

Furthermore, a result when a “waveguide” is formed by providing a linear defect in the surface structure layer 31 is shown. 13, by forming a region having a sufficient length to surface defects of the width W _d, is a top view of the surface structure layer 31B which is formed a waveguide 322. When a numerical calculation is performed on the three-dimensional photonic crystal 30 using the surface structure layer 31B, as shown in the photonic band diagram of FIG. 14, the frequency of the mode gap (the white region portion in the graph). A waveguide mode could be formed in the region. Further, it was shown that the waveguide band can be controlled by changing the defect width W _d of the waveguide 322. The waveguide 322, the defect width W _d is more than 0.40A, in the range of less than 0.60A, was the single mode waveguide. Further, when the defect width W _d above 0.60A, higher order mode is formed on the high frequency side.

The band diagram in the case where the 0.52a width W _d of the waveguide 322 shown in FIG. 15. As shown in this figure, by setting the defect width to W _d = 0.52a, a waveguide band can be obtained in almost the entire frequency band of the mode gap. In addition, the optical electric field distribution around the waveguide in this case is shown in FIG. From this figure, it can be seen that light is localized in the vicinity of the waveguide 322 and propagates through the waveguide 322.

DESCRIPTION OF SYMBOLS 10 ... Three-dimensional photonic crystal 11 ... Rod 12, 121, 122, 123, 124 ... Stripe layer 125 ... Stripe layer 13 nearest to surface structure layer ... Light mode 20 ... Prism 21 ... Bottom surface 30 of prism ... Surface structure Layered 3D photonic crystal (surface effect 3D photonic crystal)
31, 31A, 31B ... surface structure layer 32 ... connecting member 321 ... surface defects (point defects)
322: Waveguide

Claims (5)

One or a plurality of layers on the surface of a three-dimensional photonic crystal having a periodic structure in which stripe layers in which rods are arranged in parallel with each other at a predetermined period length are stacked so that rods of the adjacent stripe layers are orthogonal to each other The surface structure layer made of a stripe layer has a connecting member for connecting adjacent rods in the stripe layer, and the connecting member is arranged in the longitudinal direction of the rod at the periodic length, whereby the surface structure surface effect three-dimensional photonic crystal, wherein a photonic band gap is formed in the layer.   2. The surface effect three-dimensional photonic crystal according to claim 1, wherein an optical resonator composed of point defects is formed on the surface structure layer.   3. The surface effect three-dimensional photonic crystal according to claim 1, wherein an optical waveguide made of a linear defect is formed in the surface structure layer. Periodic structure of the three-dimensional photonic crystal, woodpile type Der having a structure in which the rod ends of the next adjacent stripe layer is displaced parallel to and half period is, the rod Ru consists high dielectric refractive index than air The surface effect three-dimensional photonic crystal according to any one of claims 1 to 3. The surface structure layer is composed of a single stripe layer, and the connecting member is formed at a position shifted by a half period from a rod constituting the stripe layer closest to the surface structure layer, and has a predetermined width, surface effect three-dimensional photonic crystal according to claim 4, wherein the formed Turkey dielectric.